Audio Sync Issues Using Timecode in Final Cut Pro

I've started editing a feature in FCP, but I've run into an audio syncing issue. This is my first time trying to sync audio and video from different sources, so bear with me. I drag everything into the Final Cut Pro explorer window, find the corresponding audio and video clips, select them, and choose Modify->Merge Clips..., and choose Timecode in the pop-up where it asks merge using what. The problem is, the merged clip isn't really synced. The video is at the beginning of the clip (with the camera audio track), there's a 50 minute gap, and then the audio clip. It's consistent for all the audio and video. Am I doing something wrong? Can I not use timecode to merge the clips? The production slate was a Denecke TS-3EL Timecode Slate, and the camera was a RED ONE.

I also tried choosing Aux Timecode 1 and Aux Timecode 2 in the pop-up after choosing Merge Clips..., but the net result is the same.